Quadrant homing system



8. J. ERST ETAL QUADRANT HOMING SYSTEM Jan. 24, 1961 3 Sheets-Sheet 2Filed May 1. 1957 W NF JOKFZOO 440m Y F- N R O T T A INVENTORS. STEPHENJ. ERST GEORGE E. BOWDEN BY self-propelled rocket.

United States Patent 2,969,018 Patented Jan. 24, 1961 QUADRANT HOMINGSYSTEM Stephen 'J. Erst, New Haven, Ind-., and George E. Bowden,Plainview, N.Y., assignors to International Telcphone and TelegraphCorporation Filed May 1, 1957, Ser. No. 657,038

6 Claims. (Cl. 102-50) This invention relates to guided missiles and isparticularly directed to homing systems for the missiles.

Photoelectric cells have now been developed which are quite sensitive toradiations in the visible and near visible portions of the spectrum.Further, such cells can now be made with relatively large planarsensitive areas, and the current through the cell, or voltage generatedby the cell, is approximately proportional to the area illuminated.Accordingly, the terminal voltage of the cell can be made analogous tothe shaded area of the cell in a field of given intensity.

The object of this invention is to provide a homing system for a missilewhich effectively utilizes the extended sensitive faces of photocells.Photocells, as used hereinafter, refer to radiation sensitive elements,such as lead sulphide or selenium layers deposited on a metal sheet.

The objects of this invention are attained in a missile having fourextended planar photocells orthogonally arranged in a plane normal tothe missile axis and optically shielded from each other by two flatopaque sheets on mutually perpendicular diameters of the missile barrelwith the line of intersection of the sheets coincident with the missileaxis. The sheets extend forwardly of the plane of the photocells so thatthe photocells are equally illuminated only when the target-source ofillumination is in line with the missile'axis. The signals from the fourcells are compared and appropriate forces applied to the aerodynamiccontrol surfaces of the missile to turn the missile toward the targetline of sight.

The above-mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will be best understood by reference to the following descriptionof an embodiment of the invention taken in conjunction with theaccompanying drawings, wherein:

Fig. l is a three-dimensional vector diagram of the coordinates of theguidance system of this invention;

Fig. 2 is a perspective, partly sectioned, view of a missile embodyingthis invention;

Fig. 3 is a blockdiagram of the control circuits of this invention;

Fig. 4 is an alternative block diagram of the circuits embodying thisinvention;

Fig. 5 is an end view of a missile of this invention; and 1 Fig. 6 is adiagram of an energization circuit used in the system of Fig. 4.

Y The missile contemplated by this invention is an elongated tubularbarrel 1, shown in Fig. 2, with orthogonal aerodynamic control fins 2.and 3. The fins may have aerodynamic-type control surfaces 4 and 5. Themissile may be of the free-flight projectile type, or may be a At theforward end of the missile is the pointed dome 6 of a material which istransparent to the radiations of the target upon which the missile is tohome. In a plane perpendicular to the missile axis are placed two pairsof extended planar radiation sensitive elements, or photocells, A, B, Cand D. Opaque shields 7 and 8 are mutually at right angles, with theirintersecting line coincident with the missile axis. The shields extendforwardly of the plane of the photocells so that the four photocells areequally illuminated only by a source on the extended missile centerline.The shields are in the plane of the control surfaces and the signalsfrom the photocells are compared and appropriate forces applied to thecontrol surface to bring or keep the missile on the target line ofsight.

Referring more particularly to the embodiments shown in the drawing, theprinciples of this invention become apparent. In Fig. l is shown inthree-dimension perspective view the coordinate system upon which thesystem of this invention operates. The missile is assumed to have avelocity component along the Y axis. The XY plane will be referred to asthe horizontal plane, although it is not necessarily related to theearths horizon. The X--Z plane is vertical in that it is perpendicularto the XY plane. The position of target T, in space, and forwardly ofthe missile may be defined by projecting the line of sight 10 into saidhorizontal and vertical planes. The projected lines 311 and 12 willthen, respectively, define the vertical or elevation angle B above orbelow the horizontal plane, and the angle of azimuth, B in thehorizontal plane. The homing system of this invention readsquantitatively the two angles B and E and generates voltages analogouseither to these angles or to the tangents of these angles. It will beassumed hereinafter that opaque shield 7 and control surfaces 3 -5 arein the XY plane, and the shield 8 and surfaces 24 are in the verticalplane. The shields are at right angles, intersecting on the missile axisand extend forwardly of the plane of the photocells A, B, C and D bydistance a. Circumferentially around the missile is the skirt 15, alsoof opaque material and of a height b above the photocell plane. Itfollows that the shields will cast shadows on two or three of thephotocells when the source of illumination is displaced from theextended missile centerline.

The planar photocells are assumed to be uniformly sensitive throughouttheir surfaces so that the voltage at the terminal of the cell isproportional to the area of the cell illuminated, or shaded, for anyreference value at the source. 7

In Fig. 3 is shown a system for producing control surface defiectionproportional to the tangent of B and B The signal from cells A and B areadded by coupling the terminals of A and B together. Likewise, C and D,in the lower-hemisphere, are added together and subtracted from A-+B inthe subtractor 20. The selector 21 receives both combined signals andproduces at its output a voltage proportional to the maximum of eitherA+B or C+D. The's'electors may comprise, for example, a conventionaldual cathode follower with a common cathode resistance. In divider 22the ratio of the difference voltage at the output of the subtractor andthe maximum voltage at the output of the selector is obtamed. This ratiois proportional to tan B Tan Bg, is then applied to a control system 23of any desired design, such as a conventional synchro, the output ofwhich isapplied to elevators 3. If desired, roll control 'may besuperimposed upon the elevators 3-3 as by a gear system 24 fordifferential control of surfaces 3-3 by the output of a gyro in the rollcontrol unit 25.

. Rudder control in the other plane is obtained in like manner. Signalsfrom cells A and D are added, and signals from B and C are added. Thedifference between the two combined signals is obtained in subtractor30, while the maximum of the two is obtained in selector 31. The ratioof the dilference signal to the maximum signal,- in the output ofdivider 32, is proportional to 3 tan B The output of the control system33 is applied to rudders 22.

The rudder and elevator control signals are isolated from each other bymeans of suitable mixing, isolation and coupling circuits represented bythe blocks A, B, C and D, respectively: typical such circuits areillustrated and described on page 10, section 19, of ElectronicDesigners Handbook by Landee, Davis, and Albrecht, published in 1957 byMcGraw-Hill.

In the embodiment shown in Fig. 4, the radiation sensitive elements andshields are so shaped that the output controls will be proportional to Band E respectively. These outputs are differentiated and compared withthe output of a rate gyro so that guidance corrections at the controlsurfaces are proportional to the angle of deviation of the target lineof sight from the missile axis. Ln Fig. 4 the shields-are assumed to berectangular and the outside edges of the planar photocell elements A,B,C and D are formed by two arcs whose equations are of the form:

where x=horizontal distance of boundary point from missile axisy=vertical distance of said point from missile axis a=height of shieldabove element plant K=arbitrary constant determined by maximum angle Bor B for which system must operate The radius of the circle enclosingthe photocells is taken as unity.

In the system of Fig. 4, the missile will home accurately when B or Bare equal to or less than thirty degrees (30). For greater values of13,, and B the missile will tend to react as if B and B were constant.In this embodiment, selector 21 selects the maximum signal from theindividual photocells A, B, C and D and obtains the ratio of thismaximum signal with the difference signals A minus B (AB) and D minus C(D-C). The two subtractors and 20a are connected to the two pairs ofphotocells, as shown. The double throw, multiple pole switch 27 isconnected between the selector and subtractors, on the one hand, thedividers 22 and 22a on the other hand. The switch may be thrown ineither of two directions, depending upon the quadrant from which themaximum signal is obtained. The direction of throw of the armatures ofswitch 27 may be made depending upon the energization of winding 28.

Fig. 6 shows one energization circuit for coil 28. Selectors for maximumA and B and maximum C and D could be connected, respectively, to thecontrol grid 40 and cathode 41 of a thyratron-type amplifier. The coil28 comprises the load impedance for the tube.

The three upper contacts u will be closed if A or B is a maximum amongthe signals A, B, C, and D. The down contacts d will close if either Cor D is a maximum among the four signals A, B, C, and D. Hence,the'output of divider 22 is proportional to A minus B (AB)/ maximum, andthe output of divider 22a is proportional to D minus C (DC) /maximum,either of which is proportional to B,,. The B signal is differentiatedin the ditferentiator 29 and is added to the output of the gyro 29a. Theoutput of the rate gyro is preferably a voltage proportional to theangle velocity of the missile about a vertical axis through the missile.The difierentiated B value is added to the rate gyro output in thecontrol circuits 23 and applied to the horizontal control surfaces 22.

A similar channel is provided for developing the B signal forapplication to the vertical control surfaces 3--3. Here, the selector 31is identical to selector 21. The functions of the two selectors may, infact, be combined in one circuit. The subtractors 30 and 30a, however,derive the A minus D (AD) and B minus C (BC) signals, respectively. Thesignals thus obtained are compared in dividers 32 and 32a to develop Aminus D (A -D)/maximum and B minus C (BC)/maximum, respectively, eitherof which is proportional to the line of sight angle B Contacts u ofswitch 270 are closed if either A or D is a maximum of the four signalsA, B, C, and D. The down contacts d are closed if either B or C is amaximum among the signals A, B, C, and D. The B signals aredifferentiated in differentiator 29', are combined with the output ofrate gyro 29a, converted to control forces in the control system 33, andapplied to the vertical control surfaces 33.

The systems shown in Figs. 3 and 4 will require a roll rate limiter. Toomuch roll could produce interaction between the channels and eventuallybring about instability of the system. Since all systems will have afinite response time, it is necessary for reliable operation that duringthis response time the missile does not roll too much.

In the embodiment shown in Fig. 5, the radiation sensitive elements areessentially point photocells. Where the same control is desired in eachdirection, the elements are placed on lines bisecting each quadrant asfar from the missile axis as feasible. Here, also, the shields arerectangular in shape, their forward ends lying in a plane perpendicularto the missile axis. The outputs of the two adjacent elements are addedand, together with the sum of the outputs of the other two elements, arefed into the computer, as described above. Such a system will have nooutput if both inputs have signal or if neither input has a signal. Ifone input has a signal and the other does not, the computer will producea positive output; whereas, if the other input has a signal when thefirst does not, there will be a negative output. The output signals arefed through a control system which deflects one pair of the controlsurfaces through a presetangle in a direction such that the missile willturn toward the target. That is, this system has the characteristic ofapplying no control if B is less than a predetermined angle dependingupon the design of the nose of the missile, and of developing a constantturning moment if B is greater than said angle. By placing shieldsaround the elements as on the circumference of the missile barrel, thecharacteristic of the system can be changed so that no control will beapplied when the'line of sight exceeds another angle design into thehead. No roll control per se is required here.

It will be readily understood that Figs. 3 and 4 are one line,informational-flow type schematic diagrams, the conventional mixing,isolation and coupling devices and circuits being represented by theblock diagrams A, B', C and D, respectively.

While the principles of the invention have been described in connectionwith specific apparatus, it is to be clearly understood that thisdescription is made only by way of example and not as a limitation tothe scope of the invention.

What is claimed is:

1. In combination, in a homing missile having a barrel with adjustableaerodynamic control surfaces: four extended planar photocells A, B, Cand D disposed in a plane perpendicular to the barrel axis; opaqueplanar shields disposed between and forwardly of the photocells so thatthe cells of each adjacent pair are uniformly illuminated only when aradiation source is located along a line coincident with the axis ofsaid barrel and are differentially illuminated by said source ofradiation when the same is displaced from said coincident line; meanscoupled to said cells for generating a voltage proportional to thedifference between the signals provided by pairs of cells; means coupledto said generating means for comparing the difference voltage with themaximum voltage of either pair to provide the ratio thereof; and meanscoupled to said comparing means for applying forces to the controlsurfaces proportional to said ratios.

2. In combination in a homing missile: an elongated barrel with a noseand tail structure; orthogonal control surfaces on said tail structurefor guiding the missile in two dimensions in flight; two pairs ofside-by-side planar radiation sensitive elements A, B, C, and Dpositioned in said nose structure; right-angle planar shields opaque toradiant energy positioned between said elements, means coupled to saidelements for deriving voltages A, B, C, and D proportional,respectively, with the illumination of elements A, B, C, and D; firstand second computer circuits coupled to said elements including meansfor deriving voltages (A+B) minus (C+D) and (A +D) minus (B+C)respectively; first means coupled to said deriving means for isolatingthe maximum of (A +3) and (C+D); second means coupled to said derivingmeans for isolating the maximum of (A+D) and (B+C); a first dividercoupled to said first computer circuit and said first isolating meansfor generating a voltage proportional to the ratio of (A+B) minus (C+D)and the first mentioned maximum; a second divider coupled to said secondcomputer circuit and said second isolating means for generating avoltage proportional to the ratio of (A+D) minus (B+C) and the secondmentioned maximum; and means coupled respectively to said first andsecond dividers and responsive to the two ratio voltages, respectively,operatively coupled to said control surfaces for operating the same.

3. In combination, in a homing missile: two pairs of planar photocellsA, B, C, and D orthogonally arranged in a plane perpendicular to themissile axis; opaque planar shields arranged between and forwardly ofsaid cells; a selector circuit coupled to said photocells for selectingthe maximum voltage of each pair; a subtractor circuit coupled to saidphotocells for deriving voltages proportional to the dilference betweenthe two pairs of voltages, a divider circuit coupled to said selectorand subtractor circuits for generating a voltage proportional to theratio of the diiference voltage to said maximum voltage, and meanscoupled to said divider circuit for controlling one of said controlsurfaces in response to the ratio voltage.

4. The combination defined in claim 3 further comprising anotherselector circuit coupled to said photocells for selecting the maximumvoltage among A+D and B-l-C, another subtractor circuit coupled to saidphotocells for deriving the difference between A+D and B-i-C, anotherdivider circuit coupled to said other selector and subtractor circuitsfor dividing said maximum voltage into said difference voltage, andmeans coupled to said other divider circuit for applying the lastmentioned voltage to the other control surface.

5. In combination, in a homing missile: four extended planar photocells,A, B, C, and D, symmetrically arranged in a plane perpendicular to theaxis of the missile; opaque shields disposed so that said photocells areuniaformly illuminated from a target source of radiant ;energy locatedon a line coincident with the axis of the missile and said photocellsare diiferentially shaded when said target source is displaced from saidcoincident line; selector circuit coupled to said photocells forselecting the maximum signal among signals, A, B, C, and D; first andsecond subtractor circuits coupled to said photocells for deriving A--Bsignals and D-C signals, respectively; a first means for deriving theratio of A-B and said maximum signal; second means for deriving theratio D-C and said maximum signal; means for selectively coupling saidfirst and second deriving means "to said first and second subtractorcircuits and to said selector circuit respectively; means coupled tosaid first and second deriving means for differentiating the ratiosignals; and means coupled to said differentiating means for applyingthe differentiating signals to one control surface of a missile.

6. The missile defined in claim 5 further comprising: a second selectorcircuit coupled to said photocells for selecting the maximum signalsamong signals A, B, C and D; third and fourth subtractors coupled tosaid photocells for deriving, respectively, voltages A-D and B-C; thirdmeans for deriving the ratio of AD and said maximum; fourth means forderiving the ratio of B-C and said maximum; means for selectivelycoupling said third and fourth deriving means to said third and fourthsubtractor circuits and to said second selector circuit respectively;means coupled to said third and fourth deriving circuits fordifferentiating the last mentioned voltages; and means coupled to saidthird and fourth deriving means for applying the differentiated voltagesto the other control surfaces of the missile.

References Cited in the file of this patent UNITED STATES PATENTS2,060,201 Hammond Nov. 10, 1936 2,415,348 Haigney Feb. 4, 1947 2,418,137Noell Apr. 1, 1947 2,457,393 Mufliy Dec. 28, 1948 2,520,433 RobinsonAug. 29, 1950 2,741,181 Marks Apr. 10, 1956

